Ammeters

1

1965 Mustang

Member
Perhaps someone can help, I have a 1937 Chevy Truck with the original 6volt electrical system (I know his is a Ford forum but I am not currently on any Chevy forums-and it is probably about the same between Chevy and Ford on this issue)
Except for the starter the electrical system goes thru the ammeter.
My electrical system is completely dead but when I put a jumper across the two terminals at the back of the ammeter, the entire electrical system comes back to life. Obviously there is some kind of an open in the ammeter (ammeter burned out?) I have cleaned and tightened the connections on the back of the gauge. I have not yet opened up the gauge to look-also a new ammeter is a little hard to find. My question is if I bypass the ammeter what is the downside? The ammeter of course won't work and reveal a discharge or a dead short. My proposed Mickey Mouse repair would not be permanent and I would someday get around to replacing the ammeter. Thanks
 
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I think what it is your main power is running in one side of the ammeter and out the other side. What they have is the Ammeter is hooked up in the main power wire. You can by pass the ammeter or just unhook the wire and hook the wires to get here. this will work to you get a new ammeter. hope this helps.
 
40cpe said:
Connect both wires on one terminal and "forgetaboutit".
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That's probably what I would do, too. There are several schools of thought about it, but the Ron Francis wiring company doesn't recommend ammeters. Doesn't think they're as safe as running without an ammeter.
 
Your ammeter, as opposed to the Ford's, has a shunt connected to the terminals. Except for starter, all current goes through the shunt. When you connect across the terminals and the circuit come to life, it indicates a missing shunt. Only Chev will know the resistance value of the shunt. But it will be much less than an ohm.
 
Red98 said:
Your ammeter, as opposed to the Ford's, has a shunt connected to the terminals. Except for starter, all current goes through the shunt. When you connect across the terminals and the circuit come to life, it indicates a missing shunt. Only Chev will know the resistance value of the shunt. But it will be much less than an ohm.
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To: Red 98 What is this shunt likely to look like? There is a heavy rectangular piece of something (looks like a fiber/bakelite insulating piece) on the outside of the back of the gauge going between the 2 outside terminals - underneath where the wires attach. Maybe this has a built in resistance and is now an open even though it looks intact? The 1937 car schematic shows a fuse on the ammeter but I could not find one. Perhaps that rectangular piece/possible shunt acts as a fuse? Thanks
 
The shunt let´s a certain % of the current go into the meter and the rest pass.
When the shunt burns all current tries to go into the meter coil...which burns up in a blink...
Usually you need to get a new meter if they are coil based..

Just took a look at a unit for sale and they seem to be magnetic...
Plenty for sale...found 5 doing a quick google run...not to bad priced either...i would look for a new unit..
 
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flatheadmurre said:
The shunt let´s a certain % of the current go into the meter and the rest pass.
When the shunt burns all current tries to go into the meter coil...which burns up in a blink...
Usually you need to get a new meter if they are coil based..

Just took a look at a unit for sale and they seem to be magnetic...
Plenty for sale...found 5 doing a quick google run...not to bad priced either...i would look for a new unit..
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Flatheadmurre: Are you saying you found ammeters for 1937 Chevrolets that are more than just electrically the same? I need something that works/fits and does not alter the original look of my truck/instrument cluster in any way. Please provide a link to these plentiful units (which I assume you mean are new ammeters.) Thanks
 

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Some ammeters have an internal shunt. These are common on older vehicles and tractors. A shunt wire can be used but a person needs to know what length the wire has to be to get the correct resistance. A shunt wire is generally connected in to the power wire from the alternator or generator to the buss and approximately in the middle of the buss feed wire with a crimp type butt splice terminal. Resistance needed for a shunt is dependent on system voltage. A person can also make a shunt wire and connect it between the two ammeter terminals.

This is a good link to info: https://www.rc-electronics-usa.com/current-shunt.html
 
Most people and all modern manufacturers run voltmeters for that reason. If the voltmeter fails if will not put the car out of commission. Plus they can pick up the voltage reading from under the dash instead of running a heavy pair of wires back to the battery or starter solenoid. I like to use both, I can't have too many old chrome Stewart Warner gauges in my cars.


When my friends and I were sixteen, poor and trying to build muscle cars we would go from junkyard to junkyard, back when you were allowed to roam free. We would look for those Stewart Warner gauges in cars. There were quite a few muscle cars in junkyards. We would remove the gauges and throw them over the fence. Later that night we would comeback and get them. I would never do anything like that today, it hurts too bad to try and lay under the dash. I've had three shoulder surgeries so I might not be able to throw the gauges over the fence and I can't see very well in the dark. What, you thought I was going to say I matured and grew a conscious.

I had a '65 Mustang with a Stewart Warner Ammeter that everything ran through except the starter. Somebody broke into it in the middle of the night and stole the ammeter, they stole all the gauges. The whole car was dead. I had to bolt the two ammeter wires together so I could get to work. I had put a lot of effort into getting those gauge. Damn thief's!
 
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Burned out shunt. Wire across it and then install an under the dash expanded scale voltmeter. You can get all the info you need from it.
 
Back in the sixty's my fathers wrecker being a 1936 1 1/2 ton Chevy we towed for the
town. So we needed more emergency lights. So I put a delco alternator of that time,
probably 35 or 40 amps. to go 12vt neg ground. All I did was the alt. output was tied in
the origional 6vt generator output wire. Therefore nothing was changed, amp gauge
showed charge and discharge. However I had to put a radio schack diode from ignition
to excite the alt without diode truck wouldn't shut off (back feed) so sound like your
amp meter is dead. As said - to bridge the amp meter probably find a 6vt voltmeter if
you can find one. My mind says those AC gauges were used a few years think they were
brown and cream??? Also couple yrs ago my Model T amp gauge went dead, same thing all went dead same as your problem...sam
 
Big Job,
If I leave the ignition switch in Accessory on the '34 coupe, the battery drains quickly. The truck is flathead with 12 volt negative ground and GM type alternator. There are no accessories, so I presume it is draining through the alternator. Tried a different starter switch and , like you, the engine would not shut off.

What capacity diode did you use, and how is it wired.

Pardon me for hijacking the thread, but it was a Chevy question!
 
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